Ferroso-ferric oxide for magnetic impulse record members



Jan. 2, 1962 J. W. AYERS ETAL FERROSO-FERRIC OXIDE FOR MAGNETIC IMPULSERECORD MEMBERS Original Filed April 1955 I) -L l E -lO r- I00 400 I000F5000 |0,000 I5,000

FREQUENCY IN CYCLES PER SECOND INVENTOR$ JOSEPH W. AYERS ROBERT A.STEPHENS ATTORNEYS United States Patent Ser. No. 75,899

14 Claims. (Cl. 252-625) This invention relates to compositions ofmatter containing very fine size crystalline particles of ferrso-ferricoxide of plate-like structure of definite minimum relative dimensions,bound together in the form of a smooth surfaced film or equivalentmember. More specifically, it relates to compositions of outstandingperformance characteristics when used as or incorporated in magneticimpulse record members in the form of discs, sheets, cylinders, movingpicture films, tapes, bands, electronic computer components andtelemetering equipment. Although the ferroso-ferric oxide particles heldtogether by a suitable resin or other bonding medium may be used as aseparate film for recording magnetic impulses, it is preferred that theoxide and bonding medium be employed in the form of a coating upon anon-magnetic backing of cellulose acetate or other carrier such as paperor a flexible resin, which tapes possess the novel outstanding magneticcharacteristics hereinafter set forth.

Prior to the advent of the present invention and over a period ofseveral years, the assignees of the instant application with theassistance of the present applicants have been engaged in the extensivemanufacture of magnetic iron oxides used in the fabrication of soundrecording tapes and other magnetic impulse recording members. The ironoxide material employed has been composed essentially of eitherferroso-ferric oxide or gamma ferric oxide, in the form of fine-grained.acicular or needle-like particles derived from synthetically prepared,non-ferromagnetic, crystaline particles of alpha ferric oxide monohydrate either by reduction alone, or by reduction followed by mildoxidation, respectively.

Although the recording members containing these oxides have performedsatisfactorily in many respects, the members are lacking in severalqualities which contribute to their unsatisfactory or limitedperformance in several fields.

A primary object of the invention is to produce magnetic impulserecording members possessing the good qualities of high coercive force,high remanence and other desirable properties of the oxides now on themarket and also possessing greater maximum performance in terms ofout-out due to the greater magnetic induction that can be induced in themedium per unit of volume.

The prior recording members having a coating of the acicular iron oxideparticles show a precipitous drop-off in signal output at highfrequencies in the range of ten thousand cycles and above. Anotherobject of the present invention is to provide recording members which donot shown this weakness, thus avoiding the necessity for the use ofcompensating electronic circuits in attempts to overcome this weakness.

Another object is to provide magnetic impulse record members especiallysuitable for recording and reproducing television and video programswhere very high frequencies are employed.

The invention may be broadly defined as encompassing magnetic impulserecord members comprising a binding medium having therein aferroso-ferric oxide in the form of very fine-grained plate-likecrystalline particles having a length to width ratio of more than 1 to 1and a width to ICC thickness ratio of at least 3 to 1, which oxide isderived from particles of synthetic gamma ferric oxide monohydrate, ofcorresponding dimensions, by reduction imparting the desired magneticproperties.

The novel, improved properties of the record members of the invention ascompared with the already known members hereinbefore described areattributed to the use of the synthetic gamma ferric oxide monohydrateparticles (a ferromagnetic material) of novel dimensions in theproduction of magnetic oxide. The magnetic oxide itself produced fromthese particles possesses a degree of superiority as to the desiredmagnetic properties but its performance characteristics whenincorporated in magnetic impulse record members, surprisingly, is muchsuperior to any quality expected.

Practically considered, the record members provide uniform signal outputat frequencies over an extended range or up to about 10,000 cycles andmore per second, and furthermore have a utilizable signal output overthe whole frequency range up to 20,000 cycles, such being particularlyimportant when the member is used for purposes such as video programrecording.

The starting material for the production of the recording members of theinvention may be described more exactly as synthetic, fine-grainedmagnetic gamma ferric oxide monohydrate plate-like particles having alength of five or less microns and a length to width ratio of more than1 to l and a width to thickness ratio of at least 3 to 1. Typically thisgamma ferric oxide monohydrate has a high coercivity and a lowremanence. For example, the coercive force will normally range from250-300 oersteds and the remanence from 5-20 gauss, as determined bysymmetrical cyclical magnetization of the material to a maximum appliedmagnetic field strength or H value of 1000 oersteds. Better performanceis obtained from recording members when the particles used in theprocess have a length to width ratio of at least 5 to 1 and bestperformance when at about 10 to 1. As to the width to thickness ratio, 5to 1 gives better results. The particles of the indicated thickness areso thin that they are transparent when viewed under the microscope underlighting conditions showning acicular particles made from alpha ferricoxide monohydrate to be opaque.

This very fiat shape of the original particles and their relativedimensions must be and are carried through to the ferromagnetic ironoxide particles on or in the record members and apparently contribute tothe superior magnetic qualities revealed. Although the importance of acertain length to width ratio in acicular or needle-like particleswherein the a and b axes of the particles are of the same orsubstantially the same dimensions has heretofore been recognized, theeffect of the ratio of length and width to thickness has not heretoforebeen considered or at least its importance ascertained. The muchdiminished third dimension of the plate-like ferromagnetic iron oxideparticles imparted through the initial use of the ferromagnetic gammaferric oxide monohydrate particles constitutes a feature of theinvention when resolved in terms of the improved magnetic properties ofmagnetic impulse recording media containing the same.

The mass of the very small crystalline gamma ferric oxide monohydratesused in the production of the ferrosoferric oxide can be preparedadvantageously in a two step process, the first involving thepreparation of a seeding material and the second the production of theoxide particles by growing the same under controlled conditions upon theseeding material.

Sixty-three pounds of ferrous chloride are introduced into an agitatingtank and suificient water is introduced to bring the volume to 350gallons. The temperature of the solution is raised to F. and thereupon adilute solution of sodium hydroxide is introduced into the tank over afive minute period, during agitation of its contents. The amount ofsodium hydroxide introduced is 28 pounds and its concentration may bevaried from one-half to one pound per gallon. Air is bubbled through theresulting mass at the rate of 20.c.f.m. for a period of about one hourduring which oxidation of the ferrous precipitate continues, causing thecolor to change from a dark blue into a green and finally into abrownish yellow. When the color has changed to yellowish tan, the airflow rate is reduced to about c.f.m. and its introduction into theslurry is continued for an additional hour or somewhat more, at whichtime the production of the seeding material is complete.

This seeding material and 220 pounds of ferrous chloride at about twopounds per gallon concentration together with 35 pounds of zinc chlorideat a concentration of about 3 pounds per gallon are introduced into areactor containing scrap iron in substantial excess of the amount whichwill be reacted. Sufficient water is then added to bring the operatinglevel to about 1250 gallons. Thereupon the contents of the reactor areagitated and oxidized by the introduction of a stream of air of about 80c.f.m. The temperature of the mass in the reactor is increased to about140 F. and maintained at this level during the oxidation which takesfrom about 24 to 48 hours.

At this point, the contents are removed and washed free of solublesalts, using decantation or filtration. The washed oxide is finallyfiltered and dried by conventional procedures. The product obtained iscomposed of platelike crystalline particles of substantially uniformsize of about one micron and less in length, the ratio of length towidth being about 10 and more to l and the apparent ratio of width tothickness being at least 4 to 1, the plates appearing to be transparent.

Other methods of producing suitable gamma ferric oxide monohydrateparticles are known and described in the literature and may be used inplace of the above described process, the only requirement being thatthe conditions of production be adjusted and controlled such thatparticles of required size and dimensions are obtained. In general, ironsalts other than ferrous chloride may be used as the starting material,such as ferrous sulfate. Also other alkalies may be used in the place ofsodium hydroxide such as ammonium hydroxide. Pyridine or aniline may beused as the alkaline reacting agents. Retarding agents appear to behighly advantageous in preventing the seeding material from changing tothe goethite or needle-like particle form, examples of retarding agentsbeing zinc chloride (as already disclosed), zinc sulfate, sodiumchloride and ammonium chloride.

The gamma ferric oxide monohydrate particles of the required size anddimensions are then converted to ferroso-ferric oxide by the action ofhydrogen at a high temperature under conditions which change theorthorhombic crystal structure into a spinel crystal structure. Severalprocedures for accomplishing this conversion are known and are describedin the literature. Suitable reduction techniques are disclosed, forexample, in US. Bureau of Mines Bulletin No. 425 (1941). The conversionmay be accomplished in the following way:

The dried mass of the gamma ferric oxide monohydrate prepared asspecifically outlined herein is pulverized by a mild grinding operationto break up the clusters, and then, to accomplish the reduction, themass of small particles is fed into a rotary kiln and heated, while theindicator-controller temperature registers from 600 to 1000 F. Hydrogenis introduced into the kiln tube in known manner, thereby to provide aferroso-ferric oxide product having a ferrous iron content ofapproximately 23%. The reduced particles are discharged from the kilntube through a water-cooled screw conveyor.

The ferroso-ferric oxide thereby obtained has a coercive force of350-450 oersteds and a remanence of about Ferroso-ferric oxide 3 Methylabietate-maleic glycol ester 60 Vinyl resin (13% vinyl acetate-87% vinylchloride copolymer) 120 A plasticizer (a linear high molecular weightpolyester resin prepared by the reaction of a dibasic acid with adihydric aliphatic alcohol) 60 Methyl isobutyl ketnne 500 Toluol 300After being ground, the mass is mixed with an additional 200 parts oftoluol and applied in accordance with known practice to a celluloseacetate base in the form of an 8-12 inch wide strip. While the appliedcoating is still wet, it is run through a magnetic field to orient theparticles in known manner after the strip is dried, calendered,compressed and burnished and finally it is slit and put on rolls orreels under tension, the normal film thicknesses being from about 0.30to 0.60 mil, and in this specific instance, being 0.55 mil.

Using a magnetic tape testing machine containing all necessary auxiliaryequipment for evaluating tapes, the new tape of the present inventionwas carefully tested and compared with a sample of high grade generalpurpose tape having thereon an acicular ferroso-ferric oxide film ofknown type (of the same 0.55 mil thickness) which had all-roundsatisfactory performance characteristics, this tape being referred to asStandard. The new tape and the Standard tape were compared as to theirfrequency response including flatness of response, magnitude of responseand uniformity of response; also as to their signal to noise ratio,their signal to direct current noise ratio, and their saturated signalto noise ratio, and also their peak-bias. The new tape was outstand ingin flatness of response over a wide range of frequency and in signal tonoise ratio at high frequencies, and it compared favorably with theStandard tape in all other tests.

The comparative frequency response is brought out in the followingtable:

Frequency response test results Frequency in Cycles per See 1,000 5,00010,000 15,000

Decibel Output of:

New Ferroso- Ferric Oxlde- Standard Ferroso-Ferrlc Oxldo The frequencyresponse of the tape of the present in vention is also recorded in theaccompanying drawing on semi-logarithmic graph paper. With reference tothe drawing and as well to the table it will be observed that the signaloutput of the new magnetic tape is substantially uniform at frequenciesup to more than 10,000 clcles per second and that the tape has autilizable output over the whole frequency range up to about 20,000cycles per second. (Deviation of plus or minus about one decibel isinconsequential in practical operation.) From the table it will also beobserved that the signal output of the Standard begins to fall offprecipitously at 5000 cycles.

The advantages of the magnetic impulse record members of the presentinvention may be summarized as follows:

(a) The signal output of the members is considerably greater at highfrequencies than that of the comparative standard when employed inidentically the same way in the same type of medium having equal filmthickness.

(b) The members have adequate signal output at desirable high frequencylevels of ten kilocycles and above. This quality makes the recordmembers especially effective where high fidelity audible response isneeded and particularly where only high frequencies are used in videoreproductions.

Because of the greater output and other qualities, the record members ofthe invention in the form of magnetic tapes may be operated at a slowerspeed particularly in the recording of video programs. For this reasonthere is less wear on the recording, play-back, and erasing heads of therecording apparatus and there is less wow, flutter and distortioncreated by the mechanical movements of the tapes.

(d) The particles of the magnetic iron oxide used in the production ofthe record members of the invention are free of objectionableaggregation, are easily dispersed in the bonding medium in which theyare suspended and respond readily to orientation. These qualitiesincrease the magnetic capacity of the record member and thus increaseits output. The thin plate-like shape of the particles of the magneticoxides greatly lessens the voids present in the medium and accordinglythe magnetic capacity of the member is materially improved over theperformance of members containing acicular particles. Greater packingdensity and greater magnetic induction apparently follow from thelamination and foliation of the thin plate-like particles of themagnetic oxides used.

(e) The frequency response of the magnetic oxide in the magnetic impulserecord members of the invention is sufiiciently uniform throughout theentire frequency range that for most purposes the necessity forproviding very elaborate compensating electronic components foradjusting electric circuits'to correct the magnetic impulse output toovercome irregularities at different positions in the sound spectrum isavoided.

(f) The record members of the invention can be used in some instanceswhere those made with conventional oxides cannot, as where the internalnoise of the circuit in which the members are to be used is equal to orhigher than the intensity of the signal induced into the electroniccircuit. Since the output of the standard and other prior members dropsoff at 10,000 cycles, the signal may wash out completely at 15,000cycles, particularly at slow tape speeds. At frequencies between thesefigures, the energy output may be so small that it is below the noiselevel of the apparatus, and in this case, the record member isworthless. In contrast thereto, the impulse record members of thepresent invention show higher output over the whole range of frequenciesand this means that the record members have a wider range ofadaptability and a greater utility.

(g) Magnetic tapes can be produced having thinner coatings of oxide,this quality being of substantial importance in the recording of videoprograms where linear speeds of from 100 to 200 inches per second areimportant. Hence the problem of handling large reels of tape is reduced.Thin coatings are desirable for economic reasons and lesser quantitiesof raw materials are required-thus they cost less.

(it) They are superior to known members because of low distortion andlow noise levels for the particles of fiat or plate-like shape aresubstantially more uniform in size and they are substantially free fromlarge oversize particles. The fiat character of the particles makes itpossible to provide a more even and regular surface upon the magneticimpulse record members. Since the induced signal on the members at highfrequencies is a skin or surface effect and the surfaces of the membersare very smooth, there is less distortion in the impulses and signals.Because of an improvement in the packing arrangement of the plate-likeparticles in the binding medium, layers of the same thickness can beprovided having'greater output.

The particles of the magnetic oxide of this invention in or on therecord members are of optimum small size to provide most efiectivecoercive force and remanence. The length-breadth ratio of theseplate-like particles is such that high magnetic induction is obtained.The coercive force of these magnetic oxides is sufiiciently low underworking conditions of magnetic recording processes that induced magneticsignals thereon may he satisfactorily erased.

It should be understood that the present invention is not limited to thespecific details disclosed herein except in the respects herein setforth, for it includes variations which will occur to those skilled inthe art upon consideration of the general teachings of the invention andthe scope of the claims appended hereto.

This application is a continuation of our application Serial No. 840,200filed September 15, 1959, now abandoned which in turn is a continuationof our application Serial No. 499,718 filed April 6, 1955, and nowabandoned.

We claim:

1. A composition of matter comprising very small, flat crystallineparticles having a length of not more than five microns offerroso-ferric oxide of spinel crystal structure bound together in theform of a smooth-surfaced film, the dimensions of said particles beingessentially in length to width more than 1 to 1 and in width tothickness at least 3 to 1, said particles being formed by the reductionof ferromagnetic gamma ferric oxide monohydrate particles oforthorhombic crystal structure and of substantially the same relativedimensions.

2. A magnetic impulse record member having a substantially uniformsignal output at frequencies up to at least about 10,000 cycles persecond comprising a binding medium having therein a syntheticferroso-ferric oxide formed from a synthetic, ferromagnetic gamma ferricoxide monohydrate, said ferroso-ferric oxide consisting essentially ofvery fine-grained, plate-like crystalline particles having a length ofnot more than five microns, also having a length to width ratio of morethan 1 to 1 and a width to thickness ratio of at least 3 to 1.

3. A magnetic impulse record member comprising, a binding medium havingtherein a synthetic ferroso-ferric oxide formed from a synthetic,ferromagnetic gamma ferric oxide monohydrate, said ferroso-ferric oxideconsisting essentially of very fine-grained, plate-like crystallineparticles having a length of not more than five microns, also having alength to w-idth'ratio of more than 1 to l and a width to thicknessratio of at least 4 to l and having a coercivity of from about 250 to600 oersteds and a retentivity of from about 1500 to 2500 gauss.

4. A magnetic impulse record member comprising, a binding medium havingtherein a synthetic ferroso-ferric oxide produced from a synthetic,ferro magnetic gamma ferric oxide monohydrate by reduction of saidmonohydrate, said ferroso-ferric oxide consisting essentially of veryfine-grained, plate-like crystalline particles having a length not morethan five microns, also having a length to width ratio of at least 5 to1 and a width to thickness ratio of at least 3 to 1.

5. A magnetic impulse record member having a utilizable signal outputover the whole frequency range up to 20,000 cycles per secondcomprising, a binding medium having therein a synthetic ferroso-ferricoxide formed from a synthetic, ferro magnetic gamma ferric oxidemonohydrate, said ferroso-ferric oxide consisting essentially of veryfine-grained, plate-like crystalline particles having a length of notmore than five microns, also having a length to width ratio of at least5 to l and a width to thickness ratio of at least 3 to 1.

6. A magnetic impulse record member having a utilizable signal outputover the whole frequency range up to 20,000 cycles per secondcomprising, a non-magnetic strip having thereon an attached trackcontaining a binding medium having therein a synthetic ferrosoferricoxide formed from a synthetic, ferro magnetic gamma ferric oxidemonohydrate, said ferroso-ferric oxide consisting essentially of veryfine-grained, plate-like crystalline particles having a length of notmore than five microns, also having a length to width ratio of more thanto 1 and a width to thickness ratio of at least 3 to 1 and having acoercivity of from about 250 to 600 oersteds and a retentivity of fromabout 1500 to 2500 gauss.

7. A magnetic impulse record member for video and other high frequencytranscriptions having a high signal to noise ratio and an effectivesignal output at frequencies in the range of 5000 to 20,000 cycles persecond comprising a binding medium having therein a syntheticferroso-ferric oxide formed from a synthetic, magnetic gamma ferricoxide monohydrate, said ferroso-ferric oxide consisting essentially ofvery small, fiat crystalline particles having a length of not more thanfive microns, also having a length to width ratio of at least 5 to 1 anda width to thickness ratio of at least 3 to l.

8. A magnetic impulse record member having a utilizable signal outputover the whole frequency range up to 20,000 cycles per secondcomprising, a binding medium having therein a synthetic ferroso-ferricoxide formed from a synthetic, magnetic gamma ferric oxide monohydrate,said ferroso-ferric oxide consisting essentially of very fine-grained,plate-like crystalline particles having a length of not more than fivemicrons, also having a length to width ratio of at least 5 to 1 and awidth to thickness ratio of at least 3 to 1.

9. A magnetic impulse record member having a substantially uniformsignal output at high frequencies up to at least 10,000 cycles persecond comprising, a nonmagnetic strip having thereon an attached trackcontaining a binding medium having therein a synthetic ferroso-ferricoxide formed from a synthetic, magnetic gamma ferric oxide monohydrate,said ferroso-ferric oxide consisting essentially of very fine-grained,plate-like crystalline particles having a length of not more than fivemicrons, also having a length to width ratio of at least 5 to 1 and awidth to thickness ratio of at least 4 to 1 and having a coercivity offrom about 250 to 600 oersteds and a retentivity of from about 1500 to2500 gauss.

10. A magnetic impulse record member having a substantially uniformsignal output at frequencies up to at least about 10,000 cycles persecond comprising, a binding medium having therein a syntheticferroso-ferric oxide formed from a synthetic, magnetic gamma ferricoxide monohydrate, said ferroso-ferric oxide consisting essentially ofvery fine-grained, plate-like crystalline particles having a length ofnot more than five microns, also having a length to width ratio of morethan 5 to 1 and a width to thickness ratio of at least 3 to 1.

11. A magnetic impulse record member having a substantially uniformsignal output at frequencies up to at least about 10,000 cycles persecond comprising, a binding medium having therein a syntheticferroso-ferric oxide formed from a synthetic, magnetic gamma ferricoxide monohydrate, said ferroso-ferric oxide consisting essentially ofvery fine-grained, plate-like crystalline particles having a length ofnot more than five microns, also having a length to width ratio of 10 to1.

12. A magnetic impulse record member having a substantially uniformsignal output at frequencies up to at least about 10,000 cycles persecond and having a utilizable signal output over the whole frequencyrange up to 20,000 cycles per second comprising, a binding medium havingtherein a synthetic ferroso-ferric oxide formed from a synthetic,magnetic gammaferric oxide monohydrate and said ferroso-ferric oxideconsisting essentially of very fine-grained, plate-like crystallineparticles having a length of not more than five microns, also having alength to width ratio of more than 1 to 1, and having a coercivity offrom about 250 to 600 oersteds and a retentivity of from about 1500 to2500 gauss.

13. A synthetic ferroso-ferric oxide formed from a synthetic, magneticgamma ferric oxide monohydrate and consisting essentially of very smallcrystalline particles of fiat, plate-like shape having a length of notmore than five microns, also having a length to width ratio of more than1 to 1 and a width to thickness ratio of at least 3 to 1, said particleshaving a coercivity of from about 250 to 600 oersteds and a retentivityof from about 1500 to 2500 gauss, said particles when fabricated into amagnetic impulse tape providing a substantially uniform signal output upto about 10,000 cycles per second and a utilizable signal output overthe whole frequency range up to about 20,000 cycles per second.

14. A magnetic oxide for the production of magnetic impulse recordmembers comprising, a synthetic ferrosoferric oxide formed from asynthetic magnetic gamma ferric oxide monohydrate and consistingessentially of very small crystalline particles of plate-like shapehaving a length of not more than five microns, also having a length towidth ratio of more than 5 to 1 and a width to thickness ratio of atleast 4 to 1, said particles having a coercivity of from about 250 to600 oersteds and a retentivity of from about 1500 to 2500 gauss.

References Cited in the file of this patent UNITED STATES PATENTS2,694,656 Camras Nov. 16, 1954 FOREIGN PATENTS 675,195 Great BritainJuly 9, 1952

6. A MAGNETIC IMPULSE RECORD MEMBER HAVING A UTILIZABLE SIGNAL OUTPUTOVER THE WHOLE FREQUENCY RANGE UP TO 20,000 CYCLES PER SECONDCOMPRISING, A NON-MAGNETIC STRIP HAVING THEREON AN ATTACHED TRACKCONTAINING A BINDING MEDIUM HAVING THEREIN A SYNTHETIC FERROSO-FERRICOXIDE FORMED FROM A SYNTHETIC, FERRO-MAGNETIC GAMMA FERRIC OXIDEMONOHYDRATE, SAID FERROS-FERRIC OXIDE CONSISTING ESSENTIALLY OF VERYFINE-GRAINED, PLATE-LIKE CRYSTALLINE PARTICLES HAVING A LENGTH OF NOTMORE THAN FIVE MICRONS, ALSO HAVING A LENGTH TO WIDTH RATIO OF MORE THAN5 TO 1 AND A WIDTH TO THICKNESS RATIO OF AT LEAST 3 TO 1 AND HAVING ACOERCIVITY OF FROM ABOUT 250 TO 600 OERSTEDS AND A RETENTIVY OF FROMABOUT 1500 TO 2500 GAUSS.